This invention relates generally to impact printers and specifically to the character carrying print elements employed in serial impact printers. The invention at hand is a new and improved article of manufacture referred to as a print wheel.
Impact printers receive their name from the use of hammers or the like to impact a slug against an ink carrier and a record medium--usually 20- pound bond paper--backed by a platen. The platen is the anvil for the hammer's blow. The ink carrier is conventionally a ribbon, i.e., an elongated web impregnated with ink. The ink is transferred to the paper record medium when the two are brought into intimate contact under the blow of the hammer. Ink is released from the ribbon in raised areas on the slug corresponding to the shape of a character. Broadly, a serial impact printer is one in which a line of print is inscribed one character at a time. Classic examples of serial printers are the familiar office typewriter, teletypewriter printers and low speed computer output printers. Other classic impact printers include calculating machines such as adding machines and business accounting machines which use mostly numerical characters.
Printing elements for serial printers shaped generally in the form of a wheel or the like have been known for some time. By way of example, see U.S. Pat. Nos. 2,236,663 (1941), 3,461,235, 3,498,439, and 3,651,916. Recently, the Diablo Corporation, a subsidiary of the present assignee, has marketed a serial printer under the trade name Hytype Printer I which has a printer wheel having a plurality of slugs located at the ends of spokes or beams extending radially outward from a hub. The print wheel is rotated by a servo mechanism to position selected characters opposite a hammer and ribbon at a printing station. A printer of this type is disclosed in a U.S. patent application filed Sept. 4, 1973, in the name of Andrew Gabor, Ser. No. 394,072, titled "High Speed Printer with Intermittent Printer Wheel with Carriage Movement" being a continuation of an application filed Feb. 25, 1972, Ser. No. 229,314, the disclosures of which are incorporated by reference into this specification. The Hytype Printer I has enjoyed commercial success as an electronic printer capable of high speed and versatile operation. The print wheel it employs is basically a single element structure in that the beams and slugs are an integrally molded thermoplastic structure. This print wheel delivers superior performance with very favorable economics, i.e., the integral wheel is relatively inexpensive to manufacture. Nonetheless, when subjective standards of print quality are encountered in certain applications, the integral-structure print wheel does not always give the desired print quality.
Specifically, in automatic text editing typewriter applications the demands on a print wheel are great. In the text editing or office typing environment, the demands for high print quality cause the print wheel to be subjected to about 10 times greater force due to about five times greater hammer energy compared to a Hytype printer operating as a computer output terminal, for example. Text editing machines include a printer, a keyboard and an electronic controller having some form of memory or storage. A typist enters character information into the memory and/or creates a copy on the typewriter printer at from 0.5 to 2.0 characters per second (cps). The type information is manipulated by the electronics to correct errors and arrange format, and an edited document is automatically typed by the printer under control of the electronics at speeds upward of 15 cps. Clearly, in this environment, the print wheel is asked to perform in manual and automatic modes which are distinct if for no other reason than on basis of speed. Of course, the user generally expects like print quality whether the machine is operated at a 2 or 20 CPS rate.
A plastic, integral print wheel performs satisfactorily in both the low and high speed and energy modes mentioned above but not with the same print or image quality over the same life span. Loss in image quality is generally judged as the first fall off in image resolution detectible by the unaided eye. The composite print wheel of this invention, on the other hand, performs excellently over even a broader range of operating conditions than those mentioned above.
Accordingly, it is a primary object of the instant invention to develop a print wheel suitable for a wide range of impact printing environments.
Another object of this invention is to obtain high print quality in document creation equipment employing a print wheel impact printer along the presently described vane.
Yet, another object of the current invention is to increase the life span of print wheels of the present type.
Another object of the invention at issue is the construction of a print wheel having significantly improved mechanical and functional features over prior print wheel designs.
Yet, another object of this invention is to depart from the design construction of prior art print wheels by building a composite print wheel made up of at least two components including the spoke or beam structure having character slugs attached to the end of the beams.
Still, another object of the present invention is to design a print wheel having character slugs whose print surfaces are capable of withstanding repeated high energy blows from a hammer yet being attached to beams which have excellent deflection properties to permit the slug to be deflected to and from a record medium by a hammer for printing.
Yet, a further object is to devise a slug structure for a print wheel that includes two separate sections. One section is for carrying the impact surface engageable by a hammer and the other section for coupling to a spoke. The use of separate sections imparts added life to a slug because the impact portion or section withstands most of the stresses created by the hammer's blow. This protects the bond holding the slug to the end of the beam from the hammer action.